Tetranitratoborate

Tetranitratoborate is an anion composed of boron with four nitrate groups. It has formula [B(NO₃)₄]⁻. It can form salts with large cations such as tetramethyl ammonium nitratoborate,^[1] or tetraethyl ammonium tetranitratoborate.^[2]

The ion was first discovered by C. R. Guibert, M. D. Marshall in 1966 after failed attempts to make boron nitrate.^[1]

The related molecule, boron nitrate B(NO₃)₃, has resisted attempts to make it, and if it exists it is unstable above -78 °C.^[2]

Other related ions are the slightly more stable tetraperchloratoborates, with perchlorate groups instead of nitrate, and tetranitratoaluminate^[3] with the next atom down the periodic table, aluminium instead of boron ([Al(NO₃)₄]⁻).

Formation

Tetramethyl ammonium chloride reacts with BCl₃ to make (CH₃)₄NBCl₄. Then the tetrachloroborate is reacted with N₂O₄ at around -20° to form tetramethyl ammonium nitratoborate, and other gases such as NO₂Cl and Cl₂.^[2]

Another mechanism to make tetranitratoborate salts is to shake a metal nitrate with BCl₃ in chloroform at 20 °C for several days. Chloronitratoborate [Cl₃BNO₃]⁻ is an unstable intermediate.

MNO₃ + BCl₃ → M[Cl₃BNO₃]

4M[Cl₃BNO₃] → 3M[BCl₄] + MB(NO₃)₄]^[4]

Properties

The infrared spectrum of tetramethyl ammonium nitratoborate includes a prominent line at 1612 cm⁻¹ with shoulders at 1582 and 1626 cm⁻¹ attributed to v₄. Also prominent is 1297 and 1311 cm⁻¹ attributed to v₁, with these vibrations due to the nitrate bonded via one oxygen.^[1]

The density of tetramethyl ammonium nitratoborate is 1.555. It is colourless and crystalline. As tetramethyl ammonium nitratoborate is heated it has some sort of transition between 51 °C and 62°. It decomposes above 75 °C producing gas. Above 112° it is exothermic, and a solid is left if it is heated to 160 °C.^[2]

Tetramethyl ammonium nitratoborate is insoluble in cold water but slightly soluble in hot water. It does not react with water. It also dissolves in liquid ammonia, acetonitrile, methanol, and dimethylformamide.^[1] It reacts with liquid sulfur dioxide.^[1][5]

At room temperature tetramethyl ammonium nitratoborate is stable for months. It does not explode with impact.^[1]

Alkali metal tetranitratoborates are unstable at room temperature and decompose.^[4]

1-Ethyl-3-methyl-imidazolimium tetranitratoborate was discovered in 2002. It is an ionic liquid that turns solid at -25 °C.^[6]

References

1. 1 2 3 4 5 6 Guibert, C. R.; M. D. Marshall (1966). "Synthesis of the Tetranitratoborate Anion". Journal of the American Chemical Society 88 (1): 189–190. doi:10.1021/ja00953a051. ISSN 0002-7863. 
2. 1 2 3 4 Titova, K. V.; V. Ya. Rosolovskii (1970). "Tetraalkylammonium nitratoborates". Bulletin of the Academy of Sciences of the USSR Division of Chemical Science 19 (12): 2515–2519. doi:10.1007/BF00854900. ISSN 0568-5230. 
3. ↑ Jones, CJ Bigler (2007). Transition and Main Group Metals Applied to Oxidative Functionalization of Methane and Use as High Oxygen Carriers for Rocket Propellants. ProQuest. p. 139. ISBN 9780549231066. Retrieved 3 February 2014. 
4. 1 2 Titova, K. V.; V. Ya. Rosolovskii (1975). "Reaction of nitrates of monovalent cations with BCl3". Bulletin of the Academy of Sciences of the USSR Division of Chemical Science 24 (10): 2246–2248. doi:10.1007/BF00929774. ISSN 0568-5230. 
5. ↑ C.C. Addison and D. Sutton. Progress in Inorganic Chemistry 8. p. 216. 
6. ↑ Jones, C. Bigler; Ralf Haiges; Thorsten Schroer; Karl O. Christe (2006). "Oxygen-Balanced Energetic Ionic Liquid". Angewandte Chemie International Edition 45 (30): 4981–4984. doi:10.1002/anie.200600735. ISSN 1433-7851.